Usually, a window lift system for a vehicle window comprises a driving motor, a lift device for moving up or down the glass of the window, and a force transmission structure for transmitting rotation of the output shaft of the motor to the lift device. The transmission structure comprises a drive plate and a shaft coupled to the drive plate. The drive plate is connected to the output shaft of the motor via a gear train. The shaft is connected to the lift device via a pinion attached to an end of the shaft and meshed with a gear of the lift device. In operation, the motor drives the drive plate to rotate. The drive plate drivingly rotates the shaft to thereby cause the lift device to move the glass of the window up or down.
Conventionally, the shaft is coupled to the drive plate via a cylindrical coupling end with two flat surfaces at opposite sides thereof fittingly received in a waist-shaped hole of the drive plate. Two opposite flat interfaces are formed between the coupling end of the shaft and the hole of the drive plate. In operation, two reverse forces are exerted on the two flat surfaces of the coupling end of the shaft, which will generate impact on the shaft and the drive plate to thereby generate vibration and noise.
As such, there is a desire for an improved transition structure which can solve the above-mentioned problems.